The present invention is intended for use in an environment of a self-propelled vehicle or other piece of equipment which is powered by a known form of internal combustion engine. The invention is preferably designed for use in connection with a vehicle or other equipment powered by a diesel engine
Vehicles having diesel engines include heavy-duty military and commercial vehicles such as trucks, buses, infantry vehicles, tanks, tractors, bulldozers, and others. Because such vehicles can be operated by various operators having different skill levels, considerable warning and protection equipment is incorporated into such vehicles. This warning and protection equipment includes means for informing an operator of the operations and conditions of certain vehicle and engine components. Additionally, diesel engines are used in a multiplicity of other applications such as trains and electricity generator sets, which all require glow plug control systems.
Diesel engines have no spark plugs or spark ignition but, rather, rely primarily upon compression ratios higher than gasoline spark ignition engines with associated compression heating, residual engine heat from prior combustion, and ambient temperature to a lesser degree for creation of combustion conditions and temperatures sufficiently above the flash point of the diesel fuel which when injected under high pressure into the vehicle combustion chambers will spontaneously ignite so as to burn completely. The fuel/air mixture of a cold diesel engine will not ignite and/or run efficiently. Varying conditions (some widely varying) including: Engine temperature, ambient air temperature, ambient air absolute density, mass air flow, engine compression ratio, and fuel flash point temperature (being also some interrelated function of the above variable conditions) require various amounts of supplemental heat to be added to the combustion chamber prior to and during engine cranking and warmup to enable fuel ignition with sufficient combustion for engine operation during engine cranking conditions and cold engine warm up operation. To assist in bringing the combustion chambers above the necessary minimal operational temperature and/or to supply a source of combustion chamber ignition temperature, diesel engine glow plug heaters, otherwise called glow plugs, are employed.
Excessive glow plug power energization time causes higher than desired glow plug temperatures which can result in significantly shortened life of the glow plugs, in addition to wasting of energy and unnecessary long time before the engine can be started. Insufficient glow plug power ON time will cause lower than desired glow plug temperatures and reduced supplemental heat which can result in: Inability to start engine, excessive cranking time, starter motor wear, undesirable hydrocarbon exhaust emissions, white smoke of incompletely combusted fuel, increased fuel consumption,
With many controllers, when a single glow plug burns out to an open circuit, the other glow plugs subsequently operate with slightly higher voltage resulting in an increased chance for a second glow plug to burn out to an open circuit, resulting in an additional higher voltage, resulting in an additional chance for a third glow plug to burn out, and so on such that the cycle can potentially continue until all of the glow plugs are burned out or have their life significantly shortened by excessive temperature due to operating at higher than anticipated voltages with glow plug controller types having fixed preglow and afterglow times.
One of the most important variables contributing to glow plug heating is the applied glow plug voltage from the vehicle's electrochemical storage battery. During engine operation the output voltage and current from the alternator charging system in parallel with the battery typically lowers the net power supply system impedance while increasing the net power supply system voltage. The power supplied to a fixed value of resistance is proportional to the square of the applied voltage, so the significant range of voltages potentially applied to the glow plugs due to battery condition, voltage regulation of alternator output, alternator speed, and vehicle electrical load regulation effect is one very important variable which can be compensated for by varying the durations of preglow time, afterglow I time, afterglow II time, duty cycle ON times, and cycle period times so as to maintain more optimal glow plug temperatures. Fixed preglow and afterglow times cannot optimally control the cycling glow plug temperatures based upon the number of variables which significantly affect the need for versus the production of glow plug heat.
Diesel powered vehicles are operated by individuals with widely varying knowledge levels of glow plug heater control system functional operation and with simple glow plug control systems there exists the potential for inadvertent and/or intentional system misuse by the operator thus automatic control is needed to safeguard against potential damage and/or inefficient operation. Abnormal human-controlled repeated cycling of the run/start switch can, in some cases with typical fixed glow plug timer functions, energize successive fixed preglow times thus potentially resulting in excessive glow plug energization with excessive glow plug temperature causing a resultant reduction of glow plug life. Typical simple fixed timer based glow plug controllers are incapable of optimal control of glow plugs given the number and range of natural and human variables affecting the system.
When the RUN/START switch is switched to OFF the glow plugs are typically immediately de-energized as the relay contact between the alternator and the battery is opened. This produces a race situation. If an alternator to battery control relay contact opens before the glow plug control relay contact then an alternator-sourced load dump occurs causing an inductive energy dump into the wiring. Glow plugs typically draw approximately 150 A of current which, when sourced solely from the alternator, can produce an electronic component damaging high energy inductive voltage spike of over 100 V causing electrical noise transients and damaging energy dissipative arcing of associated control relay contacts as they switch open.
Glow plug control is of vital importance to the function of diesel engine performance. Glow plugs are considered to have limited operational life and are somewhat costly to replace. Various glow plug and engine starting controllers with simple temperature and timer based functionality exist in the market. In various ways these existing systems fall short in the area of comprehensive control functions and features including: Optimal control of glow plug operation for maximum glow plug life, monitoring and protecting of glow plug operation, and load dump protection. Typical glow plug control systems offer minimal or no diagnostic monitoring functions to indicate electrical characteristics of specific open or short glow plugs and/or potential burn out based upon changing and/or abnormal electrical characteristics. Increasing demands for improvements in reliability, performance, efficiency, engine protection, electrical system protection, system monitoring capability, system diagnostics capability, and environmental pollution reduction all support the need for development of significant improvements to functionality of glow plug control devices and systems.